1. Field of the Invention
The present invention is broadly concerned with novel, developer-soluble, hard mask compositions and methods that utilize hard mask compositions to form structures on semiconductor substrates.
2. Description of the Prior Art
As integrated circuit chip makers continue to press for higher circuit density, the process of fabricating such circuitry is constantly challenging the limits of photolithography. The most prominent achievement in recent years in this regard is the maturity of ArF technology, and the development of immersion photolithography.
Efforts in those technologies are based on the very basic principles of optical physics, i.e., projected image resolution is proportional to the numerical aperture of the projection lenses and to the reciprocal of incident wavelength. The cost of using these principles to enhance resolution, however, is a significant reduction in the depth of focus (DOF).
DOF is a very practical matter that determines the robustness of photolithographic processes and ultimately the yield of final devices. To compensate for the DOF loss, the photoresist thickness must be reduced. Unfortunately, a limit exists for photoresist thickness reduction in the traditional single-layer scheme. The limit is determined by etch depth aid selectivity of photoresist to substrate. Etch selectivities of ArF photoresists have been improved significantly in the last few years while further improvement of organic polymer-based photoresists has been marginal.
Many new photolithographic processes, such as bilayer or multilayer schemes, have been explored to reduce photoresist thickness from the aspect of etch selectivity. Another option that has been used is photoresist trimming processes through isotropic etch. The trimming process can reduce feature size beyond the capability of photolithography, and the trimmed lines, for example, can be very important for fabricating transistor gates to improve device speed. However, there are two fundamental disadvantages to this process. First, photoresist patterns are trimmed not only laterally, but also vertically. In essence, the vertical etch rate is normally as high as three times the lateral etch rate. Thus, a significant amount of the already tightly budgeted photoresist thickness is lost in the trimming process. Second, the trimming plasma will inevitably etch the underling layer. This undesired etch sometimes can be severe.